cAMP is a second messenger involved in many of the normal physiological responses of tissues. Levels of cAMP can be modulated by production, through adenylyl cyclases, or destruction, through cAMP phosphodiesterases. A large number of biochemically and pharmacologically distinct forms of cAMP phosphodiesterases (PDEs) have been found in mammalian tissues. Most tissues express more than one form of the enzyme, yet there are clear tissue specific patterns of expression. Several forms of cAMP PDE can be specifically targeted pharmacologically, and the therapeutic modulation of cAMP levels can beneficially alter the course of a variety of disorders. Because of the complexity of expression of different forms of cAMP PDE, and because of their potential as targets for pharmacological intervention, it is desirable, and probably necessary, to isolate and characterize the genes encoding cAMP PDEs. We have been exploring the RAS/adenylyl cyclase pathways in the yeast S. cerevisiae. These studies have led us to clone and characterize the yeast genes encoding cAMP PDE. As a consequence we have developed a general method for isolating mammalian cAMP phosphodiesterase genes using mammalian cDNAs cloned into yeast expression vectors and genetic selection in yeast. At least two distinct forms of mammalian PDEs have been cloned by us and expressed in yeast entirely lacking endogenous PDEs. One of these is a member of the dunce-like family of PDEs, and one is novel. We propose to characterize these and other human PDEs expressed in brain, heart and other tissues. This work has potential application for the understanding and control of a wide range of conditions including heart, circulatory and pulmonary dysfunction, mental disorders, and perhaps immunologic disturbances.